A spokesman for Ladbrokes has said the firm is "not prepared to offer long odds" on the HS2 line being subject to delays, alterations and cancellations.
The bookmaker is currently offering 4/5 that there will be delays when it comes to the opening of the service.
The government expects to complete the first phase of the high speed route from London to Birmingham by 2026, with the Manchester and Leeds extension being finished by 2033.
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Authorities have warned that the death toll is likely to rise as much of the building is yet to be searched.
The PM will sound out the possibility of new free trade agreements with Gulf states for once the UK has left the EU.
In the unexpected announcement on Monday, Mr Key said it was the "right time" to leave politics.